Amplifier recommendations for 86 dB Sensitivity Speakers

This was taken from your 2018 thread:

"I moved from a small space to a very large 950 sqft loft with 15 ft ceilings."

This is important info if this is still your space (especially the ceiling height).

DeKay

My first nice set of speakers(at least in my opinion) were the Hales Concept Two. I drove those speakers with Audio Research VT-100 amp and Audible Illusions preamp. Never had a problem driving those speakers and enjoying great music.

@mamifero There's a big difference between an amp's ability to simply drive a pair of speakers and its ability to make them sound as good as possible.  It's not about the watts.  It's about the current (i.e.  power supply).  I'm not familiar with your equipment.  However, here's an example of what this means based upon personal experience:

In a critical listening session (i.e.  shopping experience), a pair of truly outstanding Aerial Acoustics 6T (impedance 4 ohms, 3 ohms minimum, low reactance, 90 dB for 2.83 volts at 1 meter on axis) sounded absolutely sublime to my ears when fed by a truly outstanding McIntosh MC275 tube amp (75 Watts X 2 channels or 150 Watts X 1 channel).  Did the Aerial sound good, indeed very good, with a McIntosh MA5200 (100 Watts X 2 channel into 8 ohms)?  Yes.  However, my ears could hear, instantly (i.e.  no more than 3 or 4 seconds), that these speakers needed more current to perform at their best.

@mamifero The speakers you have in mind are 86dB and 4 Ohms.

Sometimes its worth considering what this looks like in terms of efficiency rather than sensitivity, since efficiency is stated in Watts rather than Voltage. This is especially important if you have a tube amplifier!

To convert from sensitivity (2.83 Volts/1 meter) to Watts you need to know the impedance of the speaker, which is 4 Ohms. 2.83 Volts is 1 Watt if the load is 8 Ohms (into 8 Ohms sensitivity and efficiency are the same thing), which means into four Ohms its 2 Watts. That's a 3dB difference, which to the ear isn't much but it represents a doubling of amplifier power. Tube amps don't double power when you cut the load impedance in half. 

Another way of looking at that is subtract that 3dB from the sensitivity spec; you arrive at 83dB. 

That is so inefficient that you may have real problems finding a musical sounding amplifier that also has enough power to drive that speaker much past a conversational level. In most rooms this means you'll want something north of 1000 Watts per channel.

If this seems hyperbolic on my part, consider that to double the apparent volume requires an increase of amplifier power by a factor of 10.

@dekay makes a good point! 

Since your amp doesn't double power into 4 Ohms this is a very practical concern. If I were you I'd consider a more efficient speaker as this combination will have the amplifier struggling all the time. If no-one has pointed this out yet, tube amps are less efficient using the 4 Ohm tap and tend to have less bass bandwidth (as well as slightly less power).

IOW I think that speaker with your amp isn't a good idea. 

@mamifero - This remains a math problem wrt having enough power to drive that particular speaker to the desired SPL for your room and listening position.

The post by @atmasphere below explains why I used 83dB in my calculations.  To his point, even my second example of a 200 wpc amplifier that doubles into 4 ohms will only drive those speakers to a SPL of about 100dB at 12 feet.  That calculation does not take into effect a larger than typical room, speaker impedance anomalies, or the desire for greater dynamic headroom so, even at 200/400 wpc you my have barely adequate power.

As a result, there is probably no way you will have satisfactory results driving those speakers with your current amplifier.  I don’t disagree with the 1,000 wpc recommended by @atmasphere, assuming he means into 4 ohms.  IOW, an amp delivering around 400 to 500 wpc into 8 ohms and doubling into 4 ohms, should be about optimal.  The Cary 500MB amps in my second system provide 500/1,000 wpc of power, and the SMc Audio monoblocks in my main system provide 650/1,000+ wpc and do an excellent job of driving Aerial LR5 speakers that have the exact same sensitivity and nominal impedance specs as the Technics speakers you are considering, while dipping to an even lower minimum impedance of 3 ohms. 

As to sound quality, IME, amplifiers do sound different from each other so, like any component, you will need to find amplifiers delivering the type of sound you want to hear. However, if you don’t get the power right, your speakers will never reach their optimal sound quality.